U.S. patent number 6,464,671 [Application Number 09/532,522] was granted by the patent office on 2002-10-15 for medical system.
Invention is credited to Sten-Olof Elver, Jan Skansen.
United States Patent |
6,464,671 |
Elver , et al. |
October 15, 2002 |
Medical system
Abstract
Implantable drug delivery system comprising a reservoir module
provided with a drug reservoir and a drug expelling means arranged
to expel a drug from said drug reservoir, and a dispenser module
comprising drug delivery means having a predetermined number of
drug delivery openings for delivering a drug, received from said
drug reservoir, to tissue. The modules are physically separate
parts and the reservoir module is provided with a first connecting
means and the dispenser module is provided with a second connecting
means, wherein, at the time of implantation, the modules are
adapted to be connected together by the first and second connecting
means.
Inventors: |
Elver; Sten-Olof (S-184 92
.ANG.kersberga, SE), Skansen; Jan (S-134 06 Ingaro,
SE) |
Family
ID: |
27484817 |
Appl.
No.: |
09/532,522 |
Filed: |
March 21, 2000 |
Foreign Application Priority Data
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Apr 28, 1999 [SE] |
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9901528 |
May 4, 1999 [SE] |
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9901608 |
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Current U.S.
Class: |
604/288.01;
604/131; 604/288.04; 604/890.1; 604/93.01 |
Current CPC
Class: |
A61M
5/14276 (20130101); A61M 5/1413 (20130101); A61M
2205/0244 (20130101); A61M 2209/045 (20130101) |
Current International
Class: |
A61M
5/142 (20060101); A61M 5/14 (20060101); A61M
031/00 () |
Field of
Search: |
;604/131,140,141,151,153,200,890.1,891.1,892.1,93.01,502,500,67,148,288.01
;128/DIG.12 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 429 141 |
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May 1991 |
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EP |
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0 672 427 |
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Sep 1995 |
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EP |
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WO 95/29717 |
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Nov 1995 |
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WO |
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Primary Examiner: Casler; Brian L.
Assistant Examiner: Rodriguez; Cris L.
Attorney, Agent or Firm: Young & Thompson
Claims
What is claimed is:
1. Implantable drug delivery system comprising a reservoir module
provided with a drug reservoir and a drug expelling means arranged
to expel a drug from said drug reservoir to a dispenser module for
delivering the drug to tissue, characterized in that said modules
are physically separate parts and that said reservoir module is
provided with a first connecting means and said dispenser module is
provided with a second connecting means, wherein, at the time of
implantation, said reservoir and dispenser modules are adapted to
be connected together by said first and second connecting
means.
2. System according to claim 1 characterized in that said first
connecting means comprises a reservoir nipple and that said second
connecting means comprises a connecting nipple wherein the
reservoir module supplies said dispenser module with the drug
liquid via said nipples.
3. System according to claim 1 characterized in that said reservoir
module comprises drug supplying means adapted to be coupled to the
dispenser module in order to supply the dispenser module with the
drug from the reservoir module.
4. System according to claim 1 characterized in that said dispenser
module is provided with a predetermined number of drug delivery
openings, wherein said predetermined number is at least two.
5. System according to claim 4 characterized in that the openings
of the dispenser module are arranged on the part of the dispenser
module adapted to be in contact with tissue.
6. System according to claim 4 in that the openings of the
dispenser module are arranged along the periphery of the dispenser
module.
7. System according to any of claim 4 in that said predetermined
number of delivery openings is four.
8. System according to any of claim 4 in that said predetermined
number of delivery openings lies in the interval 10-30.
9. Method of administrating a drug liquid to a patient using an
implantable drug delivery system according to of claim 1
characterized in that said method comprising the following steps:
i) choosing a dispenser module and a reservoir module having
predetermined characteristics depending on the prescribed therapy
of the patient; ii) connecting the chosen modules to each other;
iii) implanting the system at a patient location where the drug
should be administrated.
10. Method according to claim 9 characterized in that said method
further comprising the following step: iv) filling or refilling the
reservoir module with a drug liquid when necessary.
Description
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an implantable drug delivery
system, a dispenser module, a set of dispensing modules, a
reservoir module, a set of reservoir modules and a method of
administrating a drug using the implantable drug delivery system
according to the preamble of the independent claims.
BACKGROUND OF THE INVENTION
1. Field of the Invention
Pharmaceutical drugs can be administrated to patients in many
different ways, such as orally, nasally, through electroporation or
by injections. Injections can be intravenous, intramusculaire or
subcutaneous. The way of administration of drugs to a patient is
often depending on properties of the drug, the organ to be treated
and the patient's physical and social presumptions to control the
prescribed treatment. The efficiency of the prescribed drug
treatment is also highly dependent on the patient's abilities to
follow the prescription. It is a well-known fact that the ability
to follow a prescription is related to the patient's understanding
and knowledge of his disease and his possibility to follow the
prescribed form of treatment.
Medical treatment by subcutaneous injections during a long period
of time in patients that due to physical or social reasons
themselves cannot make the injection are requiring assistance from
e.g. a nurse or a relative.
The injection itself might have considerable side effects because a
relatively high concentration of an active substance is
administrated to one local site beneath the skin. Irritation of the
skin or local haematoma is common for some patients.
Parameters that affect how frequent the injections are taken are
the subcutaneaous half-life time for the drug, i.e. the time it
takes for half the injected dose to be absorbed by tissue, the
actual dose and of course the patient's ability to follow the
prescription.
The injected volume depends on the type of drug used and the wanted
effect of the treatment and is normally between 0,2-0,6 ml per day
given in 1-3 injections.
The costs to offer sterilized injection syringes and to discard
them after use is a considerable part of the total cost for the
treatment.
2. Description of the Prior Art
Implantable infusion pumps are well known in the art for
administrating drugs to a patient, e.g. to administer insulin to
the pancreas, pain-relieving drugs to the spinal canal or
intravenous administration of drugs against Parkinson's disease.
Below is a short summery of different kinds of implantable infusion
pumps
U.S. Pat. No. 4,193,397 discloses an implantable infusion apparatus
and method. Although mentioned the possibility of having a battery
powered electrical valve to perform the pumping action, a preferred
pump embodiment employs a valve that can be actuated
extracorporeally either manually or magnetically. Modifying the
flow rates and volumes of the apparatus components, particularly
the mixing chamber and the apparatus outlet tube, can provide a
dosage profile tailored to the patient's requirements. The
described embodiment requires the patient's contribution that,
according to the discussion above, is a major drawback.
Also U.S. Pat. No. 5,769,823 discloses an implantable infusion
pump. The purpose of this known device is primarily to provide an
inexpensively manufacturable infusion pump. This is accomplished by
arranging a plastic casing with a bellows that receives a
propellant producing a vapour pressure that exerts a pressure on
two resilient bags containing a medicament. When a throttle means
is opened a clearly defined quantity of the medicament passes out
of the bags into a catheter and into the body of a patient.
U.S. Pat. No. 4,673,391 discloses a micropump disposed within a
human body for continuously delivering small quantities of a
pharmaceutical liquid stored therein to be injected in a human
body. The control part of the pump is placed outside the body and
generates a magnetic force that can open a valve of the implanted
micropump and release the pharmaceutical liquid. A problem with
this known device is that it requires that the patient actively
controls the device, which not always is possible or desirable.
U.S. Pat. No. 5,752,930 relates to an implantable infusion pump for
administration of a pharmaceutically active agent via a catheter to
a plurality of infusion sites located at spaced intervals in a
portion of a body to be treated by the agent. The catheter is
provided with elution holes to perform the administration of the
agent. However, experience has shown that the flow rate of the
agent is not uniform through all elution holes. In particular, at
low flow rates, fluid moving down the catheter exits the catheter
at the elution hole having the least fluid resistance to flow to
that relatively little or no fluid exits the catheter through the
remaining elution holes. This results in overdose to some sites
(the elution hole with the least fluid resistance) and underdose to
other sites (remaining elution holes). The device described in U.S.
Pat. No. 5,752,930 is directed to solve that problem. The solution
is shortly to apply a first pressure to the agent in the catheter
for a first time period and a second pressure to the agent for a
second time period so that substantially the same dosage of agent
can be applied to each of the sites. One drawback with this
solution is that it is technically rather complicated in that it
requires an accurate control of the applied pressure.
One major drawback with implantable infusion pumps according to the
prior art is that they cannot easily be optimized with regard to
flow-rate of the delivered drug and the volume of drug stored in
the pump.
Another drawback with the prior art infusion pumps is that they
have a complicated structure inter alia due to that they all
administer the drug via a catheter.
SUMMERY OF THE INVENTION
It is an object of the present invention to provide an implantable
drug delivery system where the above-mentioned drawbacks are
avoided. These drawbacks are avoided by the implantable drug
delivery system, a dispenser module, a set of dispensing modules, a
reservoir module, a set of reservoir modules and a method of
administrating a drug using the implantable drug delivery system
according to the independent claims. Preferred embodiments are set
forth in the dependent claims.
The present invention makes it possible to tailor the treatment by
choosing a reservoir module and a dispenser module having a desired
performance for achieving an optimal treatment, i.e. the
possibility to administer a prescribed dose during a prescribed
time in a controlled manner.
The invention is especially useful for short term implantation for
administration of drugs during some weeks or month after a surgery,
e.g. related to hip or knee prosthesis, when the patient is
immobilized during the recovery period.
The drug is delivered to tissue through drug delivery openings that
are arranged around the periphery of the dispenser module. At least
two openings are provided. In order to provide an easy-handled
implantable infusion system the drug delivery openings are arranged
around the periphery of the implant. This is advantageous in that
no delivery catheter is needed according to a preferred embodiment
of the invention.
By arranging several openings a most advantageous drug delivery is
achieved in that only a limited volume is delivered at each
location which is favorable in that the risk of negative effect on
tissue as a result of too high drug exposure is almost eliminated.
An ideal situation exists if the limited volume delivered from one
opening is in a one to one relationship with the absorption at the
delivery site. In other word if the capillary force of the tissue
at the delivery site provides for continuous absorption of all
delivered drug at the delivery site then the ideal situation
occurs. Furthermore, according to still another embodiment of the
invention, it is possible to only use some of the delivery openings
and according to predetermined pattern "activate" different
openings at different times.
The drug supplying means comprises drug delivery channels, which is
a system of channels for providing the delivery openings with drug.
In an implantable drug delivery system it is of greatest importance
to know the exact volume of the delivered drug dose. However, in a
system with a drug delivery channel having several openings of the
same size arranged along a channel with the same inner diameter
along the channel the pressure inside the channel changes along the
channel. This pressure change results in a gradually decreasing
delivered volume when approaching the distal end of the channel
(the end most far from the drug reservoir). In order to arranged a
system where the delivered volume is controllable and almost the
same for all openings the area of the openings increases along the
channel towards the distal end according to a predetermined
relationship.
It is also possible to arrange a separate delivery channel for each
delivery opening. In that case and if they have the same length
then the area of the separate openings can be same resulting in
that the same volume is delivered from each opening.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic drawing of the implantable system
illustrating the functional principles of the present
invention;
FIG. 2 shows a cross-sectional view of the reservoir module
according to the present invention;
FIG. 3 shows cross-sectional view of the reservoir nipple according
to the present invention;
FIG. 4 shows a side view of the reservoir nipple according to the
present invention;
FIG. 5 shows a schematic drawing illustrating a delivery channel
according to one embodiment of the invention;
FIG. 6 shows a cross-sectional view of a connecting nipple of the
dispenser module according to the present invention;
FIG. 7 shows a top view of the dispenser module according to a
preferred embodiment of the invention;
FIG. 8 shows a detail of a delivery opening,according to a
preferred embodiment of the invention;
FIG. 9 shows a cross-sectional view of an alternative embodiment of
a connecting nipple of the dispenser module according to the
present invention;
FIG. 10 shows a cross-sectional view of a second alternative
embodiment of a connecting nipple of the dispenser module according
to the present invention;
FIG. 11 shows a top view of the dispenser module according to a
second preferred embodiment of the present invention; and
FIG. 12 shows a detail of delivery openings according to a second
preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The functional principles of the present invention are illustrated
by the schematic drawing disclosed in FIG. 1. FIG. 1 shows a
reservoir module 1 provided with first connecting means 2 and a
dispenser module 3 provided with second connecting means 4. Drug
delivery openings 5 are arranged along the periphery of the
dispenser module. The arrow schematically designates the flow of
drug from the reservoir module to the delivery openings of the
dispenser module. The modules are physically separate parts that,
at the time of implantation, are adapted to be connected together
by the first and second connecting means.
FIG. 2 shows a cross-sectional view of the reservoir module
according to a preferred embodiment of the present invention. The
reservoir module 1 comprises a drug reservoir 10 with a reservoir
opening provided with a drug supplying means which in this
embodiment is illustrated as a nipple including an interior valve
11, drug expelling means 12,13 and a protective casing 14 enclosing
the reservoir and the expelling means. The drug supplying means
supplies the dispenser module with a pharmaceutical drug as will be
described in greater detail below. The protective casing is made
from an inert material having biocompatible characteristics, such
as titanium, stainless steel or a composite of polymers. The drug
reservoir 10 is compressible and elastic and made of an inert
treated aluminum-laminated foil, rubber, silicone or a polymer e.g.
PVC. The material used inside the reservoir is of course approved
by the authorities for use in contact with each pharmaceutical drug
to be stored. The drug expelling means 12,13 can be arranged in
many different ways. The main function of the drug expelling means
is to exert a force on the drug reservoir so that drug is expelled
therefrom. One preferred way of achieving the necessary force is
illustrated in FIG. 2. One or many movable plate(s) are arranged to
provide a pressure on the drug reservoir. The pressure that makes
the plates to move are in turn generated by a number of springs
that provide for a constant mechanical force on the plate(s). As
can be seen from the figure, both helix-wounded springs and spring
leaves can be used. Also temperature dependent bimetal springs or a
foam rubber are possible to use. Another possibility, as shown in
the prior art, see e.g. the above-mentioned U.S. Pat. No. 4,673,391
or U.S. Pat. No. 5,769,823, is to use a liquid or a gas to exert
the pressure on the reservoir.
With references to FIGS. 3 and 4 the reservoir nipple including an
interior valve will now be described.
The reservoir nipple is manufactured in an inert material, as
titanium, glass, gold or a gold/platinium plated material or a
polymer e.g. PVC, with a threaded outside 15 and with two stop
protrusions 16, that prevent unscrewing the reservoir module from
the dispenser module when connected together. The reservoir nipple
further comprises a profiled area 17 to fixate the collapsible
inner reservoir around by a shrinking process, a supporting area 18
where the protective casing is attached by welding, a valve 19 with
two suspended claws 20 in the low end of the valve. The top of the
nipple is angled so that an injection needle can be guided towards
the upper part of the valve 21. On the lower part of the nipple two
grooves 22,23 are made to create two distinct positions for the
valve's suspended claws. The inner reservoir, prior to being filled
for the first time, is free of air e.g. in vacuum, as the valve is
locked into its upper position where the valve is closed (this
upper position shown in FIG. 3). The valve is locked in this
position by the friction of the suspended claws to the upper
groove, which friction is higher than surrounding air pressure
allowing no air to enter the inner reservoir. When filling is about
to take place, the injection needle pushes the valve to its lower
position, in which the valve is open, and the suspended claws
attach to the lower groove, allowing the vacuum pressure to assist
in filling the inner reservoir to its fullest extend.
It is important to have the possibility to control the valve from
outside the body when the device is implanted, i.e. to be able to
close the valve in order to stop the liquid distribution and also
to reopen it when desired.
One way to control the valve is by arranging a magnet into the
valve 24 making it possible with the aid of a strong external
magnet to close, if needed, the distribution of liquid from the
inner reservoir. An alternative method of closing liquid
distribution after implantation is to have the valve mounted on a
central bar equipped with a spiral spring. This bar has one thread
with one stable position where the valve is open to allow liquid to
flow to the dispenser module. By pushing the valve with the tip of
an injection needle the valve is brought out of its stable position
closing the liquid flow. The principle is analogous to how a ball
pen with a push function works. A second push by an injection
needle allows the valve to enter its stable position, whereby the
flow can continue after a temporary stop.
As described in connection with FIG. 1 is the reservoir module
connected to the dispenser module by first and second connecting
means. As briefly discussed above is the drug supplying means
arranged in the reservoir module and adapted to be coupled to the
dispenser module in order to supply the dispenser module with the
drug from the reservoir module. According to a preferred embodiment
of the present invention (as described with references to FIGS.
2-4) is the first and second connecting means integrated with the
drug supplying means. It is of course also possible to arrange the
first and second connecting means separate from the drug supplying
means (as indicated in FIG. 1).
The drug supplying means is connected to drug delivery channels in
order to deliver the drug to the openings of the dispenser module.
In order to arranged a system where the delivered volume is
controllable and preferably the same for all openings the area of
the openings increases along the channel towards the distal end
according to a predetermined relationship. This is roughly
disclosed in FIG. 5 where the delivery channel 6 and drug delivery
openings 5 are shown. As can be seen increases the area of the
openings along the channel in the direction of the drug flow (see
arrow in the figure).
It is also possible to arrange a separate delivery channel for each
delivery opening. In that case and if the channels have the same
length then the area of the separate openings can be same resulting
in that the same volume is delivered from each opening.
According to a preferred embodiment of the invention is a
combination of the above-mentioned principles of arranging the
delivery channel used.
A preferred embodiment of the dispenser module according to the
present invention provided with connecting means integrated with
the drug supplying means and also provided with preferred
arrangements of delivery channels will know be described with
references to FIGS. 6-8. FIG. 6 discloses a cross-sectional view of
a connecting nipple 25 of the dispenser module 3. This connecting
nipple is adapted to cooperate with the nipple on the reservoir
module and is preferably threaded and made in the same material as
the reservoir nipple. Two stop protrusions 26 are arranged for
engagement with the corresponding protrusions 16 on the reservoir
module in order to prevent the dispenser and reservoir modules to
be disconnected when once connected together. Two parallel plates
27 are joined together so that the drug delivery channels are
provided between these plates. There are many different ways to
provide a predetermined grooved pattern in each plate that
corresponds to the desired delivery channels. These are etching,
engraving, cutting or similar processes. The plates are preferably
made of titanium, gold, ceramic material, silicon, stainless steel
or a polymer, e.g. PVC. The connecting nipple 25 also comprises a
membrane block 28 with two membranes 29 made of an inert material
attached to the membrane block by shrinkage fit. The
above-mentioned different parts forming the connecting nipple are
welded together under pressure in order to prevent any leakage in
the assembled implanted system. The lower side of the connecting
nipple is provided with a lower supporting part 30 to support a
lower protecting casing 50 of the dispenser module. Similarly, the
upper side of the connecting nipple is provided with an upper
supporting part 31 to support an upper protecting casing 51 of the
dispenser module. The upper and lower casings are made of an inert
material and are fastened to the connecting nipple by e.g. welding.
FIG. 7 shows a top view of the dispenser module according to a
preferred embodiment of the invention. Four drug delivery openings
5 are arranged evenly distributed along the periphery of the
dispenser module. Four delivery channels, indicated by dotted
lines, supply the openings with a drug liquid. The upper membrane
of the two membranes 29 is also disclosed. In order to guide the
tip of a syringe when filling or refilling the implant with a drug
two magnets 33 are arranged on the upper side of the dispenser
module, either integrated in the connecting nipple or in the upper
protective casing. A detector that detects the magnet fields from
the magnet is connected to an apparatus for guiding the tip of the
syringe to the correct position above the membrane 29.
FIG. 8 shows in great detail one of the delivery openings according
the preferred embodiment of the present invention. The joined
plates 27 extend outside the upper and lower protecting casing
50,51. One of the plates 35 is bent around the rounded end of the
other plate so that the outflow opening 36 is protected against
pressure from the tissue that might reduce or stop the outflow. The
outflow is arranged at the peak of the rounded end of the other
plate in order to avoid that drug liquid is accumulated around the
outflow opening 36.
An alternative embodiment of the dispenser module according to the
present invention provided with connecting means integrated with
the drug supplying means and also provided with preferred
arrangements of delivery channels will know be described with
references to FIGS. 9-12.
FIG. 9 discloses a cross-sectional view of a connecting nipple of
the dispenser module. This connecting nipple is adapted to
cooperate with the nipple on the reservoir module and is preferably
threaded and made in the same material as the reservoir nipple. Two
stop protrusions 26' are arranged for engagement with the
corresponding protrusions 16 on the reservoir module in order to
prevent the dispenser and reservoir modules to be disconnected when
once connected together. The connecting nipple also comprises a
membrane block 28' with two membranes 29' made of an inert material
attached to the membrane block by shrinkage fit 32'. The
above-mentioned different parts forming the connecting nipple are
welded together under pressure in order to prevent any leakage in
the assembled implanted system. The lower side of the connecting
nipple is provided with a lower supporting part 30' to support a
lower protecting casing 50' of the dispenser module. Similarly, the
upper side of the connecting nipple is provided with an upper
supporting part 31' to support an upper protecting casing 51' of
the dispenser module. The upper and lower casings are made of an
inert material and are fastened to the connecting nipple by e.g.
welding. The embodiment described in connection with FIG. 9 differs
from the one described in connection with FIG. 6 in that a
connection 56 is provided, e.g. on the side of the connection
nipple, where a pump (not shown) is arranged instead of a direct
connection of a delivery channel (formed e.g. by plates 27 in FIG.
6). The pump receives via opening 56 a flow of drug liquid from the
reservoir module and is on its other side (downstream) connected to
delivery channels, e.g. formed by plates as in FIGS. 6-8.
FIG. 10 discloses a cross-sectional view of a connecting nipple of
still another alternative embodiment of the dispenser module. In
addition to the connecting nipple described in connection with FIG.
9 an additional connection 58 is arranged, e.g. on the side of the
nipple, for connection of a second pump. This pump is activated
when filling or refilling the reservoir module.
FIG. 11 shows a top view of the dispenser module according to a
second preferred embodiment of the invention. Several delivery
openings 5 are arranged along the periphery of the dispenser
module. A drug supplying channel 60 runs along the periphery, close
to the delivery openings, of the dispenser module in order to
supply the openings with a drug liquid. This drug supplying channel
is provided with the drug liquid from the reservoir module. This
can be performed by connecting the periphery drug supplying channel
60 to the channel(s) formed by the plates 27 as described in
connection with FIG. 6. Alternatively it is connected to one or
many pumps 38 as illustrated in FIG. 11. The embodiment disclosed
in FIG. 11 further comprises a control unit 37, a power supply 41,
e.g. a battery, and one or many valves 39. A separating wall 40 is
arranged to separate the "wet" part of the module from the control
unit and the power supply. A connection part 33 for connection of a
sensor or a heart stimulating electrode (e.g. according to the
IS-standard) can also be arranged on the dispenser module.
FIG. 12 shows in greater detail the delivery openings according the
embodiment of the present invention described in FIG. 11. The right
drawing shows a cross-sectional view of the periphery drug
supplying channel 60 and three delivery openings. The left drawing
shows a cross-sectional view of a delivery opening along line A--A
of the right drawing.
The periphery drug supplying channel 60 and the delivery openings
are preferably arranged inside a plate arrangement running along
the periphery of the module. The plate arrangement comprises two
joined plates 31 that are joined together so that the periphery
drug delivery channel 60 and the outflow channels 34 to the
delivery openings 36 are provided between these plates. There are
many different ways to provide a predetermined grooved pattern in
each plate that correspond to the desired delivery channels. These
are etching, engraving, cutting or similar processes. The plates
are preferably made of titanium, gold, ceramic material, silicon,
stainless steel or a polymer, e.g. PVC. One of the plates 35 is
bent around the rounded end of the other plate so that the outflow
opening 36 is protected against pressure from the tissue that might
reduce or stop the outflow. The outflow is arranged at the peak of
the rounded end of the other plate in order to avoid that drug
liquid is accumulated around the outflow opening 36. The outflow
channels 34 from the periphery drug supplying channel to the
delivery openings are provided with an increasing cross-sectional
area depending on the distance from reservoir module in order to be
able to deliver the same volume from each delivery opening (see
description in connection with FIG. 5).
Below is a description of a method of using an implantable drug
delivery system according to the present invention.
Depending of the therapy prescribed to a patient, e.g. the
treatment duration, social situation for the patient, the
prescribed dosage, etc., a matching pair of reservoir and dispenser
modules is chosen. The drug outflow per time unit for a particular
dispenser module can be calculated based on the number of delivery
openings, the cross-sectional area of the drug delivery channels
and the viscosity for the drug liquid. The higher dosing volume the
more delivery openings in order to minimize the dosing volume
delivered at each opening per time unit. The cross-sectional area
of an outflow channel is typically in the range of 0,01 mm to 0,1
mm. The flow-rate of the dispenser module is typically in the range
of 8-12 .mu.l/hour. The volume of the inner reservoir is typically
in the range 4-30 ml.
The dispenser module is connected to the reservoir module via the
threaded nipples by rotating the modules relative each other until
the stop protrusion engages. A needle of a syringe, filled with a
drug, penetrates the membranes of the dispenser module and opens
the valve by moving valve part 19 to its lower position. The inner
reservoir of the reservoir module is then filled due to the
under-pressure exerted by the vacuum inside the inner reservoir.
When the inner reservoir is filled with a drug, the drug expelling
means, e.g. plates and one or many springs, exert a force on the
inner reservoir that increases the pressure inside the reservoir.
The inner reservoir then expels the drug liquid to the drug
delivery channels of the dispenser module and thus to the tissue
near the implanted system. This situation persists until the inner
reservoir is so compressed that the pressure inside the reservoir
is less than the counter pressure from the tissue near the delivery
openings. It is then possible to refill the reservoir module and
the above procedure is repeated.
The present invention is not limited to the above-described
preferred embodiments. Various alternatives, modifications and
equivalents may be used. Therefore, the above embodiments should
not be taken as limiting the scope of the invention, which is
defined by the appending claims.
* * * * *